The present invention relates to improvements in methods and mechanism for making a plastic bag chain, and more particularly for making a chain of bags where adjacent bags are joined by an interconnection which has a predetermined critical breaking strength which can be controlled by the method of manufacture.
The invention relates to thin plastic film bags which have sides and a bottom edge, and at the upper end have a reclosable zipper lock structure. The zipper lock structure constitutes an interlocking rib and groove profile which is closable by applying an opposed closing pressure progressively along the length of the profile elements and which are opened by either drawing the profile apart by pulling flaps or by sliding an opening slider along the length of the profiles or by longitudinal movement of one profile relative to the other. Reclosable bags of this nature are disclosed, for example, in U.S. Pat. Nos. 3,198,228, 3,291,177, 3,338,284 and 3,340,116.
In the manufacture of bags of the above type, they are typically made by the plastic being continuously extruded from a circular die to form an endless tube. However, the bags can be made from a folded flat film with interlocking profiles at either end attached integrally or otherwise. In the tubular form, the mating interlocking profiles are formed on the inner surface of the tube. The profiles are joined when the plastic has cooled sufficiently to eliminate the distortion of the plastic. Subsequently, individual bags are formed by forming cross-seals at spaced intervals to form a seam at the side edges of each bag, and the bag is cut from the tube at the seam.
In one commercially advantageous form, the bags are manufactured from the tube, and are stored to be sold and shipped to the user who opens, fills and recloses the individual bag. These bags may be stacked in boxes, but one preferred arrangement is to cross-seal the bags in such a manner that they can remain in strip form and the individual bags torn off of the supply strip. One arrangement for utilizing such a bag is disclosed in the copending application, Ser. No. 429,617, now U.S. Pat. No. 4,490,959, dated Jan. 1, 1985, wherein automatic machinery has been devised for feeding, opening and reclosing the reclosable bags. Such mechanism utilizes a series of interconnected bags drawing them along a travel path through the work stations of the machine. At one section of the machine, the individual bags are removed from the supply chain by being forcibly torn from the chain.
Whether the interconnected chain of bags is used in automatic machinery such as above referred to, or whether the chain of bags is used manually, a factor of importance is the force which must be applied to tear the individual bags from the supply chain. If the interconnecting means is too strong, it will be difficult to tear individual bags from the supply chain, and such tearing can result in damage to the bag being removed or to the next sequential bag. If the interconnecting means is of insufficient strength, the advantages of keeping the bag supply in a chain are lost in that the chain may accidentally break, and thus becomes wholly unsuitable for automatic machinery, which must draw in the chain of bags and remove individual bags by applying a predetermined pulling force determined by the machinery design.
In this type of interconnected chain of bags, it is not only important to have the interconnecting means have a strength within the right range, but it is also very important to have the strength of attachment of the bags be uniform within certain tolerances so that in a feeding mechanism of a machine, the device can be set to apply a uniform force and uniform results be obtained.
One form of interconnection is to have the bags cut laterally from each other, but remain attached at one or more locations where the plastic is not cut. However, this type of interconnection does not always tear uniformly, and it becomes necessary essentially to fracture the entire interconnection at one time. Further, the fractured interconnection at times provides an unattractive or unsightly torn portion, and with improper tearing, the torn portion can extend into the bag to rupture the bag wall and destroy the air or moisture-tight integrity of the bag material.
It is accordingly an object of the present invention to provide an improved method and mechansim for the manufacture of a continuous bag chain wherein individual plastic bags can be torn from the supply, in such a way that the interconnection between the bags tears readily and easily and uniformly without endangering the integrity of the adjacent bags.
A still further object of the invention is to provide an improved mechanism for forming cross-cuts and cross-seals on a supply of bag tubing or folded film which has interlocked profiles on the inner surface of the tube or inner surface or edge of the film so that the bags are cut and the side seams are formed in the same operation, and so that an interconnecting junction of plastic is formed between adjacent bags with a cut or perforation of predetermined length in that junction so that the interconnecting portion of plastic which remains is of a predetermined strength and size and will rupture with the application of a uniform predetermined tearing force.
A further object of the invention is to provide an improve method and mechanism which is utilized in making a bag chain wherein the strength of attachment of the individual bags can be controlled and wherein the process can be used to provide either one or a plurality of attaching links of material.
A further object of the invention is to provide an improved method and mechanism of making a bag chain wherein the bags are attached in a chain by frangible links and the links are constructed so that they contribute to the function of the interlocking rib and groove element by permanently aligning these elements at their ends.
Other objects, advantages, and features as well as equivalent methods and structures, will become more apparent from the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in the specification, claims and drawings, in which: